I re-wrote MSPAGER for Exchange. Hoo boy what a hack that was! A VB3 app running as a service, essentially. I don't know if you remember romeo and juliet; those were PCs pulled from pc-recycle by a co-worker to serve install images.
Also, I survived Bedlam DL3 (but I didn't get the t-shirt).
see https://techcommunity.microsoft.com/blog/exchange/me-too/610... for the explanation for the Bedlam reference.